1. Field of the Invention
The present invention relates to an optical scanning device and synchronizing signal detecting method thereof, and more particularly to an optical scanning device and synchronizing signal detecting method thereof, wherein beams scanning during a procedure of converging the beams radiated from a light source unit to reach a photosensitive drum in the form of spots are partially and identically reflected in a direction opposite to a beam scanning path to be incident to the light source unit, thereby inducing signal change within the light source unit and, at this time, detecting a synchronizing signal.
2. Description of the Prior Art
Generally, in optical scanning devices, as shown in FIG. 10, beams radiated from a light source unit 1 internally equipped with a laser diode are transformed into parallel beams which are in parallel with one another in a main scanning direction and a sub-scanning direction while passing through a collimator lens 2. The parallel beams pass through a slit member 2a having a hole elongated in the main scanning direction via a portion corresponding to the hole, and then converge in the sub-scanning direction on a cylindrical lens 2b.
The beams having converged in the sub-scanning direction are incident to a deflection unit 3 to be reflected thereafter in the state of having a regular angle of view by a polygon mirror 3a which is rotated at high speed, thereby outgoing toward a focal unit 4. Here, focal unit 4 is of a scanning system lens which may consist of a toric lens 4a and a focusing lens 4b for converging to make the incident beams outgoing to a photosensitive drum 5. Here, photosensitive drum 5 is provided with an interval for forming a focus image by the scanning beams, i.e., an effective scanning width 5a, and a detection unit 6 is furnished for generating a synchronizing signal that constantly synchronizes effective scanning width 5a.
Detection unit 6 serves by detecting the beams before or after effective scanning width 5a to generate the synchronizing signal, which is equipped with a reflection mirror 6a for reflecting some of the beams outgoing toward photosensitive drum 5 into the other direction. The beams reflected by reflection mirror 6a are the beams before or after effective scanning width 5a, which are converged in the main scanning direction during a procedure of passing through a beam detect lens 6b and are incident to a photodiode 6d after passing through a slit 6c having a small aperture. Photodiode 6d detects the synchronizing signal by means of the incident beams.
In association with the conventional optical scanning device constructed as above, the beams radiated from light source unit 1 are changed into the beams of which main scanning and sub scanning become in parallel while passing through collimator lens 2. Thereafter, the beams in the sub-scanning direction converge while passing through slit 2a and cylindrical lens 2b. The beams having converged in the sub-scanning direction scan photosensitive drum 5 under the state of having the regular angle of view at polygon mirror 3a. Also, the beams converge in the main scanning direction by focal unit 4 to be formed as the spots before scanning to photosensitive drum 5 and then are incident to photosensitive drum 5.
Detection unit 6 detects the beams before or after effective scanning width 5a of photosensitive drum 5 to generate the synchronizing signal. The beams reflected from polygon mirror 3a are reflected toward photodiode 6d by reflection mirror 6a before reaching effective scanning width 5a or passing through effective scanning width 5a of photosensitive drum 5. At this time, the beams converge while passing through cylindrical lens 6b and focused while passing through slit 6c prior to being incident to photodiode 6d. Then, photodiode 6d generates the synchronizing signal in accordance with the incident beams.
However, when considering the conventional detection unit, the beams before or after effective scanning width 5a are reflected by reflection mirror 6a, and the reflected beams are incident toward separately-provided photodiode 6d, so that the synchronizing signal is detected. Furthermore, cylindrical lens 6b and slit 6c should be employed for converging the beams incident toward photodiode 6d to have drawbacks of complicating the construction and increasing the number of parts. In addition to these, photodiode 6d, cylindrical lens 6b, slit 6c and the like are to be fixedly installed into the interior of the optical scanning device to make the device bulky to hinder fabrication of the optical scanning device having a small size.